Adding a new camera layer (last build from GitHub 22Fev2016) brings the following known issues:
1- Makes everything darker on the canvas when drawing the first strokes
2- Cannot be deleted using the delete functionality

I think they added this so people wouldn’t get confused about having to select the camera layer or not. However I was thinking that if in the future we would like to have “multiple” animated cameras for a complex scene we might requrie multiple camera layers, so it’s natural to be able to delete it, regardless.

After some deliberation this has been resolved in the following manner:

Apart from the first camera layer, you can create and delete additional camera layers without raising a warning

You can’t delete a camera layer when there’s only one because Pencil2D requires the camera to exist in order to allow the animation to be exported. If you try to delete it, Pencil2d will prompt you a message that explains this.